A catheter of the prior art may be regarded as having some important technical disadvantages. For instance, the catheter has a relative wide external diameter to facilitate a catheter lumen of sufficient dimension for the flow of fluid, and requires advancement through the vessel lumen. The wide external diameter of the prior art catheter may cause (sub)obstruction of the blood flow. Additionally, the position of the catheter tip cannot be stabilised with respect to the wall of the vessel, causing a risk of dislocation of the catheter's distal tip and possible dysfunction of the catheter.
A further disadvantage of conventional catheters is damage to the vessel wall during advancement. In particular, there may be damage or irritation to the endothelium. While pushing the catheter inside a vessel lumen, the catheter's tip can either cause endothelial wall lesions or friction initiating the cascade of blood clotting, or can be deviated by a septum, causing malfunctioning or obstruction of the catheter.
As conventional catheters are advanced through the venous vessel by maintaining the catheter essentially parallel with the vessel (see FIGS. 1 and 2), clearance around the point of entry is necessary, e.g. a wide diameter burr hole through the cranium in the case of accessing the superior sagittal sinus. In adults, introducing the catheter into the sinus through a standard skull burr hole is technically cumbersome, since an oblique angle is necessary to prevent endothelial laceration of the opposite venous sinus wall and to realize a correct orientation of the catheter (i.e. ante- or retrograde to the blood stream). However, the thickness of the skull bone, requires a wide bore hole to achieve an angle sufficiently oblique. Also, in the pediatric and adult population, the positioning of the subgaleal trajectory of the shunt system is quite difficult in order to prevent kinking of the tubing and to avoid stress causing displacement of the sinusal catheter.
The evacuation of cerebrospinal fluid is necessary to treat medical conditions or illnesses. In particular those in which the physiological evacuation of cerebrospinal fluid is insufficient or disturbed such as in hydrocephalus, normal pressure hydrocephalus, benign intracranial hypertension. It may also be used to treat medical conditions in which the retention or accumulation of substances in the cerebrospinal fluid is caused by or responsible for the disease such as in Alzheimer's disease, Down's syndrome, hereditary cerebral hemorrhage with amyloidosis of the Dutch type (HCHWA-D), epilepsy, narcolepsy, Parkinson's disease, multiple sclerosis or other demyelating disease of the central nervous system, amyotrophic lateral sclerosis, brain tumors, Guillain-Barré syndrome, and the like.
Typically, evacuation of cerebrospinal fluid (CSF) is typically performed using a CSF shunt. CSF shunts in the art commonly comprise three components: (1) a catheter positioned in a cerebral ventricle or cistern, the ventricular catheter; (2) a valve preventing regurgitation of CSF into the ventricles and preventing intracranial hypotension either by exercising resistance to the CSF flow (pressure gradient valves) or by constantly adapting the CSF flow (flow regulating valves); (3) a distal catheter classically being inserted into the right cardiac atrium (atrial catheter) or into the peritoneal cavity (peritoneal catheter). The ventriculo-atrial and ventriculo-peritoneal shunts of the art are disposed with significant disadvantages set out below.
Evacuation of cerebrospinal fluid remains non-physiological. This principally due to the changing orientation of the peritoneal or atrial catheter in the lying state versus in the sitting or erect position of the patient. In the lying position, the fluid column in the distal catheter is in a horizontal orientation, creating no influence on the pressure gradient between the brain's ventricles and the intraperitoneal cavity or cardiac atrium. In the sitting or erect position, the distal catheter is in a vertical orientation. Due to gravity, this fluid column in a vertical orientation exerts the so called siphoning effect. This siphoning effect can cause over-drainage of cerebrospinal fluid causing intracranial hypotension. In the acute stage, this over-drainage can cause collapse of the brain's ventricles and acute subdural hematoma. In the chronic stage this over-drainage can cause (a) chronic (postural) intracranial hypotension with headache and/or nausea and/or vomiting and/or chronic fatigue with concentration problems and intellectual dysfunction and/or visual or auditory disturbances; (b) chronic subdural hematoma; (c) slit ventricle syndrome; (d) iatrogenic craniosynostosis with microcephaly in infants.
In normal individuals, the superior sagittal sinus and the right cardiac atrium are connected by collapsible cervical veins (the internal jugular veins), hence the venous cerebral blood flow is constantly adapted to the position or physiological condition of the normal individual, preventing the siphoning effect. In the ventriculo-atrial and ventriculo-peritoneal shunt patients, the internal jugular veins are bypassed, therefore more complex valves (variable resistance valves or flow regulating valves) and anti-siphon devices are utilised in the art, making a cerebrospinal fluid shunt much more complex, more vulnerable, and more expensive. Despite these technical improvements, a small group of patients still experience symptoms due to non-physiological cerebrospinal fluid evacuation and therefore non-physiological intracranial pressures.
Ventriculo-atrial and ventriculo-peritoneal shunts are easily obstructed causing insufficient cerebrospinal fluid evacuation and therefore intracranial hypertension. Main causes of obstruction are blood clots or brain tissue debris blocking the ventricular catheter or the valve, protein accumulation in the valve mechanism, choroid plexus ‘growing’ inside the ventricular catheter. The siphoning effect might also be responsible for a great number of the ventricular catheter obstructions by ‘aspirating’ the choroid plexus into the catheter's lumen. In growing children the catheters can block by kinking or by breaking caused by the increased tension. Also, in growing children, the peritoneal catheter's tip can be retracted into the subcutaneous fat or the atrial catheter's tip into the superior caval vein causing insufficient cerebrospinal fluid evacuation.
Ventriculo-atrial and ventriculo-peritoneal shunts have a high rate of bacterial shunt infections, with risk of bacterial meningitis or ventriculitis or cerebritis, possibly with livelong morbidity or even mortality risk. The infection rates in the implantation period are between three to seven percent.
Because of the vulnerability, complexity and high cost and non-physiological cerebrospinal fluid evacuation of the above mentioned ventriculo-atrial and ventriculo-peritoneal shunt systems, there is a worldwide medical interest for establishing a cerebrospinal fluid shunt between the ventricles or cisterns of the brain and a dural venous sinus (e.g. superior sagittal sinus, transverse sinus, sigmoid sinus). These cerebrospinal fluid shunts are known as ventriculosinus shunts. This is to obtain a physiologically adequate evacuation of cerebrospinal fluid by using the flow regulating effect of the collapsible internal jugular veins. Very important and pioneering in vitro and in vivo experiments and development of surgical techniques have been realized by professor Ismail EI-Shafei, M.D. and his son professor Hassan EI-Shafei, M.D., in Cairo, Egypt. Since 1985 prof. Ismail EI-Shafei advocates and implants the retrograde ventriculo-sagittal sinus shunt. Professor Svend Erik Boergesen, M.D. and professor Flemming Gjerris, M.D. of the University Hospital Rigshospitalet, Copenhagen, Denmark, also developed a cerebrospinal fluid shunt system shunting between the cerebral ventricle and a dural venous sinus, the so-called SinuShunt.
Disadvantages associated with ventriculosinus shunts include their obstructive size that may cause a raised venous pressure inside the dural venous sinus, may reduce the blood flow speed and thus the risk of clotting of the blood inside the dural venous sinus (sinus thrombosis). Typically a catheter that forms part of the prior art shunt will have an external diameter of 2 to 3 millimeter and an intrasinusal length of 20 to 50 millimeter, which may cause a significant obstruction of the blood flow in the accommodating vessel by its large volume (e.g. minimal 1 mm2×π×20 mm or 62.8 mm3 to maximal 1.5 mm2×π×50 mm or 353.25 mm3). Additionally, the catheter cannot be stabilized onto the sinus's wall, causing a risk of dislocation of the catheter's distal tip and possible dysfunction of the cerebrospinal fluid shunt.
Moreover, the position of catheter tip cannot be stabilised inside the sinus's lumen; it should be localised in the center of the sinus's diameter. A catheter's tip lying against the internal wall of the venous sinus has important disadvantages. The catheter is more likely to be blocked by the endothelial layer covering the internal wall of the dural venous sinus, thus causing a total obstruction of the cerebrospinal fluid shunt. Further, the catheter tip lying against the internal wall of the venous sinus cannot fully profit from the impaction effect created by the velocity of the blood flow inside the dural venous sinus as the velocity of this blood flow is maximal at the center of the sinus's diameter and minimal against the sinus's inside wall. This lower velocity of blood flow at the sinus's inside wall, again advocates the clotting of blood at the catheter's tip, blocking the cerebrospinal fluid shunt. Also, a catheter's tip in contact with the endothelial wall activates the blood clotting cascade.
While advancing the catheter inside the dural venous sinus with an intrasinusal length of 20 to 50 millimeter, the catheter's tip can easily either cause endothelial wall lesions increasing the risk of blood clotting, or can be deviated by an intrasinusal septum, causing malfunctioning or obstruction of the cerebrospinal fluid shunt.
Moreover, in the prior art, the surgeon needs to make an incision of a minimal length of 5 millimeter in the wall of the superior sinus to introduce a standard catheter inside the dural venous sinus. This increases the risk of important blood loss, the risk of aspiration of air inside the sinus possibly causing an air embolism and the risk of invagination of the endothelial layer causing obstruction to the blood flow inside the dural venous sinus.
US2008/0262406 describes a secure device for the attachment of a shunt catheter, wherein the secure attachment is to an outside wall of the peritoneal cavity. U.S. Pat. No. 3,492,996 describes a ventriculo-atrial shunt having an attachment means to an atrium of the heart. U.S. Pat. No. 4,646,752 describes an intracranial measuring screw not designed for use in a shunt.
The present invention aims to overcome the disadvantages of the art.